lib9: add newline to exec error message

R=golang-dev, bradfitz, r
CC=golang-dev
https://codereview.appspot.com/8573043
io: document non-guarantees of io.Closer

R=r, golang-dev
CC=golang-dev
https://codereview.appspot.com/8575043
encoding/json: fix handling of anonymous fields
The old code was incorrect and also broken. It passed the tests by accident.
The new algorithm is:
        1) Sort the fields in order of names.
        2) For all fields with the same name, sort in increasing depth.
        3) Choose the single field with shortest depth.
If any of the fields of a given name has a tag, do the above using
tagged fields of that name only.
Fixes issue 5245.

R=iant
CC=golang-dev
https://codereview.appspot.com/8583044
cmd/ld: fix inconsistency in internal linking of common symbols.

Some variables declared in C could end up as undefined symbols
in the final binary and have null address.

Fixes issue 5114.
Fixes issue 5227.

R=golang-dev, iant, ajstarks, dave, r
CC=golang-dev
https://codereview.appspot.com/8602044